I bought the son purely by accident! He's 6 years old ! I'm not a medical worker and it's very far from this !!! I do not need it!!

Assuming that you are posting because you’d like a refund then purchases are considered final, but you could try the 'report a problem' page to contact iTunes Support and see if they will refund or credit you as a one-off : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via page : https://support.apple.com/contact or https://www.apple.com/emea/support/itunes/contact.html